U.S. Pat. No. 3,623,933 discloses an apparatus, the operation of which involves conveying a sheet product to the nip between a pair of laminating rolls, the driving roll of which continuously rotates at a speed which can be greater than the conveyor speed. A film is supplied to the nip, and when the sheet product reaches the nip, the rotating roll grips it and the film to advance them through the nip, thereby laminating the film to the product. The apparatus and process makes no provision for heating the sheet product except by heating the laminating rolls, which then heat the sheet product through the film being laminated. A disadvantage of this apparatus and its process is when heating of the sheet product is necessary to obtain adhesion of the film to the sheet product, slow passage of the sheet product through the nip would be required for sufficient heating of the sheet product, and this slow passage may lead to undesired softening and uneven flow of the film being laminated to the sheet product.
A process is also known for laminating a photosensitive film to a printed circuit board to serve as a resist in the manufacture of a printed circuit, such as described in U.S. Pat. No. 3,469,982. Such process has involved introducing the board and photosensitive film together to the nip of a pair of heated laminating rolls, which rotate to laminate the film to the board. Rotation of the laminating rolls has been actuated by a microswitch sensing the board upstream of the nip and stopped when the board passed the switch and through the nip. This process suffered from the same disadvantage as in U.S. Pat. No. 3,623,933. In addition, the process usually involved manual feeding of the circuit boards to the laminator, which was more expensive than desired and reduced yield.
U.S. Pat. No. 3,547,730 discloses an apparatus and process in which heated laminating rolls continuously operate to laminate photosensitive film to printed circuit board fed from a supply bin containing such boards. This patent also discloses that film and or board can be fed through a preheater before being fed to the laminator, but specific apparatus and process for carrying out this preheating is not disclosed. In industry, it has been customary to do preheating by radiant heating of the circuit board such as in an oven. Often this preheating was done on a batch of circuit boards which were then successively fed to the lamination step, this operation suffering from the disadvantage of manual handling as well as temperature variation from board to board during the lamination process. U.S. Pat. No. 4,025,380 discloses conveying circuit boards through a radiant heater (Infrared-heater lamps) and then to lamination which involves stopping the movement of the board while a severed edge of the film is adhered to the leading edge of the board, and then the film and board are passed through laminating rolls to laminate the remainder of the film to the board, with the film being severed to match the trailing edge of the board prior to passing through the laminating rolls. This process suffers from the disadvantage of the two-step lamination process being complicated and the radiant preheating being inefficient and so remote from the lamination that excessive heat loss occurs. In addition, the process makes no provision for establishing alignment of the boards fed to the process unless supplied from a stack of boards or for maintaining the established alignment.
The need has arisen for greater economies in lamination, e.g., faster laminating speeds, less manual operations, greater yield, and reduced film waste which are not satisfied entirely by prior laminating techniques.